Class-A surfacing 3/3: blend curves, curved-edge fillets, the G2 corner and continuity analysis (#1642)

Thanks @midasdf.

crates/doc/src/tests.rs

@@ -113,6 +113,7 @@ fn box_fillet_cut_timeline() {
             body: None,
             style: Default::default(),
             fit: Default::default(),
+            corner: Default::default(),
         },
         None,
     )
@@ -183,6 +184,7 @@ fn errors_are_reported_not_fatal() {
             body: None,
             style: Default::default(),
             fit: Default::default(),
+            corner: Default::default(),
         },
         None,
     )